Acoustical apparatus for telephonic communication



Nov. 27, 1928. v

vw. RUDOLPH ACQUSTICAL APPARATUS FOR TELEPHONIC COMMUNICATION Filed Aug. 25 .1921

RWY I Patented Nov. 27, 1928,

ED STATES PATENT. OFFICEg] wmnnrm nunonrn, or xmn, Gunman-Y; assrenora we ran 1mm sremu. Gasmaserum in. a. 11., or Kmn, eaamnv.

AGOUSTICAL APPARATUS FOR Application flled'Auguat 25,,1921, Serial No.

In constructing such devices it has hither to been the general practice to strict1y-avoid any coincidence between their natural rates- 7 p f the invention. For both curves the abscissse m of vibration and the frequencies or groups frequencies which t cy were designed to ,re-. Above all things all ceive' or reproduce. possible care was taken to make such natural rates of vibration as might exist higher than the frequencies of the sound to. be transmitted, e. g. in talking apparatus for telephonic communication these natural rates of vibration were made higher than the principal rates of vibration occurring in human as speech.

In contradistinction to this practice the present invention contemplates. the utilization of the natural rates of vibration of such apparatus for the'purpose of improvmg the efliciency in the transmission of sound. The invention resides in constructing these sound apparatus of two or moreintercoupled vibratory structures whose naturaltuning is such that the. coupling freao uencies, i. e. the frequencies of resonance peculiar to the apparatus when its vibratory structures are coupled, form the-limits between which the frequencies lie for which the apparatus is intended.

coupling frequencies were. made to lie outside of the region of the rates of vibration to be transmitted, in order to thus obtain a good and undistorted reproduction of. the

40 sounds in question, articularly of human speech. Recent deve opments' in the art of constructing acoustical apparatus how render it possible to damp the natural rates of vibration to such an extent that, in spite of their being utilized for sound transmission,

-no disturbing distortion of the voice vibra- 4 tions occurs." On the other hand the invention enables a marked increase of the efliciency of this apparatus to be achieved. The invention will now be explained with reference to the accompanying drawing in which Fig. 1 illustrates bv 'curves the-fundar mental principle on w ch the invention is abused,

; bodies, the one bcinglthe actual microphone In the apparatus constructed hitherto the mnnnrrromc COMMUNICATION;

495,236, and in Germany September 27, 1920.

Figure 2 shows an application of the in- 'vention' to microphone receivingv trans mitters, and=Figure 3 shows an application of the invention to-, sound apparatus of the electromagnetic type-of construction. I

In Fig. 1 the curve I illustrates the acousticproperties of a modern telephone receiver of the kind now generally used. II is the resonance curve of a receiver accordin to Examples of the practical application of the invention are shown in Figs. 2'and3.

Fig. 2 is a sectional View of a capsular microphone in which-there are two vibratory 76 or energy converter and the other the diaphragm, P. The-latter has a certain natural rate' of vibration; and the former has also since it is designed in such a way that the two electrodes 0 0 form separate masses which are interconnected byelastic members, such as the bows b, b. In Fig. 3, which is a sectional view of a telephone receiver, the diaphragm P also has, of course, a certain natural rate of v1- bration, and forms one of the vibratory bodice or structures of the apparatus. The second vibratory bodyorv structure is the 8:11 7 space or chamber R, which is constructed 1n the form of, an open Helmholtz resonator having a diaphragm at one end and the open-- i'ng sat the other through which it acts upon the sound transmitting air (acoustlc duct of thear).

Instead of the said resonator or in addition to it, the parts of the electromagnet' ener -converter'may be made to act ,as the secon (or the. third) vibratory structure in which case the electromagnet would pre erably be made to consist of two parts we, and m, as shown, which operate as vibrating masses interconnected byelastic members e and c .Theelastic members may also con-. sist of diaphragms, springs or any other suitable elastic bodies.

The individual tuning of the bodies or" structures (where, for example, thevibratory consists of a diaphragm and a micro phone 'or an. 'electro-magnet) may be. made such that the natural rate of vibrationbfthe 110 .temis vibratory coupled structures,

diaphragm lies somewhat below, and that of the microphoneor electromagnet somewhat above'(but is not very different from) -the average frequency. that is to be transmitted. This tuning is indicated by the crest at c and d of the dotted lines (Fig. 1). The average frequency of the acoustic range to be transmitted lies at f. When the two vibratory bodies, whose individual or indepentures is made so great relatively to the cou pling that the depressions between the peaks 0r crests of the resonance curve of the coupled system are at a'height greater than 40 er cent .of the maximum amplitude (hig est crest) or, in other words, by suitable damping of the vibratorystructures the highest resonance peak of the coupled sysrevented from going beyond the pomt w ere it would destroy the aforesaid ratio.

The invention mayalso be accomplished by mak1n the individual tunings of the odies or structures' equal, and coupling them suitably; or by making the tunmg of the ener -converting device ower than that of the iaphra and coupling them suitably. As to this latter method, however, it may be said that as a rule, particulalry where a microphone is the energyconverter, the arrangement does not give as satisfactory resultsa's where if anything the tumng of the ener -converter is higher than that of the diagbra The term body? or dies as used in the claims is intended to include a body or bodies of air, such for example as that in chamber R (Figure 3). The reference, in the claims, to the' up er and lower frequencles of resonance 0 the coupled system, is intended to mean the frequencies on the resonance curve of the system such as b and a respectively of Figure 1.

' I claim:

1 A telephone apparatus including a lurallty of oscillator structures having defimtely proportione masses and elastic members to provide definite resonant frequencies and damping factors, means for mechanically coupling said structures together, said b virtue of the relation of the masses and elastic members, having resonant peaks between which the speech frequency lies and a coeficient of acoustic coupling" less I than the. damping factor, whereby the result-is obtained that the depressions in the resonance curve ilreabove 40% of the-highest peak of said curvei 2. A telephone apparatus having a plu rality of oscillatory structures, one structure including a sound detector, a second structure comprising a microphone, means for mechanically coupling -said structures together, each structure having a definite resonant frequency before coupling obtained by the adjustment of 'masses and elastic members, and said coupled structures having a definite coupling coeflicient obtained by adjustment of the masses of the oscillatory structures such that the speech frequencies lie within the two resonant peaks of the coupled structure.

3. A telephone apparatus having a plurality of oscillatory structures, one structure including a sound detector having a definite resonant frequency, a second structure comprising -a transmitter having a second definite resonant frequency, means for mechanically coupling said' structures together, each structure having its masses and elastic members so proportioned that the two resonant frequencies'of the acoustically coupled system lie just outside, on either side respec-- tively 'of' the speech range of frequencies.

4. A telephone apparatus having a plurality of oscillatory structures, one structure including a sound detector having a definite resonant frequency, a second structure comprising a transmitter having a second definite resonant frequency, means for mechanically coupling said structures together, each structure having its masses and elastic members so proportioned that the two resonant frequencies of the acoustically coupled system lie just outside, on either side respectively, of the speech range of frequencies, the resonant peak corresponding to the detector lying below the speech range and the resonant peak corresponding to the trans mitter lyin above the speech range.

5. An e ectrical acoustical transmitter having a plurality of oscillatory s'ructures, one structure including in combination a sound detector and a. tuned resonating chamher having a definite resonating frequency, a second structure comprising a transmitter having a second definite resonant frequency means for "mechanically coupling said structures together, each structure having its masses and elastic members so proportioned that the two. resonant fre uencies of the acoustically coupled system ie just outside, on either side rrespectively, of the speech range of frequencies. p

. n testimony whereof I aflix my signature.

WILHELM RUDOLPH. 

